290 HALES ON PERSPIRATION. [BOOK n. 



imbibed by the whole surface of the roots, viz., ^ part of an 

 inch. And the surface of the plant above ground, being 

 5616 square inches, by which, dividing the thirty-four cubic 

 inches, viz., 5 % 4 l6 =* ^--5-, this gives the depth perspired by 

 the whole surface of the plant above ground, viz., -^ T part of 

 an inch. Hence, the velocity with which water enters the 

 surface of the roots to supply the expense of perspiration, is 

 to the velocity with which the sap perspires, as 165 : 67, or 

 as -sV : Try* or nearly as 5 : 2. 



The area of the transverse cut of the middle of the stem is 

 a square inch; therefore the areas, on the surface of the 

 leaves, the roots, and stem, are 5616, 2286-1. 



The velocities, in the surface of the leaves, roots, and trans- 

 verse cut of the stem, are gained by a reciprocal proportion 

 of the surfaces. 



*$ r leaves = 5616 

 g 1 roots = 2286 

 <j I stem = 1 



= 1 J I 34 inch. 



Now, their perspiring thirty-four cubic inches in twelve 

 hours' day, there must so much pass through the stem in that 

 time ; and the velocity would be at the rate of thirty-four 

 inches in twelve hours, if the stem were quite hollow. In 

 order, therefore, to find out the quantity of solid matter in 

 the stem, July 27th, at 7 A.M., I cut up, even with the 

 ground, a Sunflower; it weighed three pounds in thirty days; 

 it was very dry, and had wasted in all, two pounds four 

 ounces ; that is, f of its whole weight. So here is a fourth 

 part left for solid parts in the stem, (by throwing a piece of 

 green Sunflower stem into water, I found it very near of the 

 same specific gravity with water,) which filling up so much of 

 the stem, the velocity of the sap must be increased propor- 

 tionally, viz., ^ part more, (by reason of the reciprocal 

 proportion,) that thirty-four cubic inches may pass the stem 

 in twelve hours; whence its velocity in the stem will be 

 45-j inches in twelve hours, supposing there be no circulation 

 nor return of the sap downwards. If there be added to 34, 

 (which is the least velocity,) | of it = 11^, this gives the 

 greatest velocity, viz., 45^-. The spaces being as 3 : 4, the 



